The present invention relates to a stepping motor and more particularly to a stepping motor which is adapted to detect one revolution of the motor shaft thereof.
As is well known in the art, the rotor of a stepping motor makes an equiangular revolution per driving pulse. Theoretically, therefore, the total angle of revolution of the rotor can be absolutely determined based on the angle of revolution per driving pulse and the total number of driving pulses applied.
In fact, however, there is occasionally a loss of synchronism, namely, a discrepancy between the actual angular revolution of the rotor and the number of driving pulses applied to the stepping motor. Because of such loss of synchronism, it is difficult to determine accurately the angular position of the rotating rotor at any given moment.
One of the measures generally taken against such difficulty in stepping motors is to provide a counter which is adapted to count driving pulses applied to the stepping motor and to be reset to its initial value every one revolution of the rotor under the influence of a reset pulse. To this end, the stepping motor is adapted to produce a reset pulse for resetting the counter every one revolution of the rotor. As a result of the provision of the counter, the fraction of revolution less than one full revolution of the rotor can be determined based on the counted value of the counter and, on the other hand, the number of revolutions is equal to the number of reset pulses. Consequently, the angular position of the rotating rotor at any moment can be easily determined based on the counted value of the counter. As will be apparent from the above, even if there is an asynchronous rotation during one revolution, the counted value which may include an error in angular position is reset every one revolution, thereby avoiding an accumulated error in angular position of the rotor. The provision of the above-described counter is contributive to the accurate determination of the number of revolutions of the rotor and/or the angular position of the rotating rotor.
To provide reset pulses, heretofore, a driven body coupled to the stepping motor has been provided with a light-opaque lug which is detected by a sensor such as a photosensor to produce a reset pulse every one revolution of the driven body. The provision of such a lug on the driven body involves the problem that the lug is apt to be damaged when assembling the driven body and mounting the assembled driven body on the rotor shaft of the stepping motor and that it is necessary to locate the sensor accurately at a predetermined position, and so a complicated assembling operation is required.